Promoter G-quadruplex folding precedes transcription and is controlled by chromatin
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ABSTRACT:
ORGANISM(S): Homo sapiens
PROVIDER: GSE162299 | GEO | 2021/03/31
REPOSITORIES: GEO
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Project description:G-quadruplexes (G4s) are noncanonical DNA secondary structures formed through the self-association of guanines, and they are distributed widely across the genome. G4 participates in multiple biological processes including gene transcription, and G4-targeted ligands serve as potential therapeutic agents for DNA-targeted therapies. However, genome-wide studies of the exact roles of G4s in transcriptional regulation are still lacking. We found that drug-induced promoter-proximal RNA polymerase II pausing promotes nearby G4 formation, and oppositely, G4 stabilization by G4-targeted ligands globally reduces RNA polymerase II occupancy at gene promoters as well as nascent RNA synthesis. To study the underlying mechanisms by which native G4 affects transcriptional regulation, we annealed the biotin-labeled core promoter DNA to form G4s and performed pull-down assays with nuclear extraction proteins in the presence or absence of TMPyP4. Mass spectrometry analysis was performed to identify the interacting proteins with G4-forming core promoter DNA.
2021-07-19 | PXD026830 | Pride
Project description:DNA secondary structures are important for fundamental genome functions such as transcription and replication1. The G-quadruplex (G4) structural motif has been linked to gene regulation2,3 and genome instability4,5 and may be important to cancer development and other diseases6-8. Recently, ~700,000 discrete G4s have been observed in naked human single-stranded genomic DNA using G4-seq, a high-throughput sequencing technique that detects structural features in vitro.9 It is of vital importance to investigate G4 structures within an endogenous chromatin context, which until now remained elusive10,11. Herein, we address this via the development of G4 ChIP-seq, an antibody-based G4 chromatin immunoprecipitation and high-throughput sequencing approach. We identified ~10,000 endogenous G4 structures and show that G4s are predominantly seen in regulatory, nucleosome-depleted, chromatin regions. G4s were enriched in the promoters and 5âUTR regions of highly transcribed genes, particularly in genes related to cancer and in somatic copy number amplifications, such as MYC. Reorganization of the chromatin landscape using a histone deacetylase inhibitor, resulted in de novo G4 formation in new and more prominent regulatory, nucleosome-depleted regions associated with increased transcriptional output. Our findings suggest a striking relationship between promoter nucleosome-depleted regions, G4 formation and elevated transcriptional activity. Comparison between normal human epidermal keratinocytes and their immortalized counterparts revealed a ï¾7-fold greater G4 abundance in immortalized cells, of which 80 % were found in regulatory, nucleosome-depleted regions common to both cell types. Consequently, cells exhibiting more G4s displayed significantly increased transcriptional output and were more sensitive to growth inhibition by a small molecule G4 ligand. Overall, our results provide new mechanistic insights into where and when DNA adopts G4 structure in vivo. Our findings show for the first time that regulatory, nucleosome-depleted chromatin and transcriptional states predominantly shape the endogenous G4 DNA landscape. Two cell lines, treated with entinostat or untreated, analyzed to detect gene expression differences, presence of G-Qudruplexes and chromatin state. Each combination of conditions replicated in duplicates or triplicates.
2016-08-05 | E-GEOD-76688 | biostudies-arrayexpress
Project description:G-quadruplexes (G4s) are four-stranded nucleic acid structures abundant at gene promoters. They can adopt several distinctive conformations. G4s have been shown to form in the herpes simplex virus-1 (HSV-1) genome during its viral cycle. Here by cross-linking/pull-down assay we identified ICP4, the major HSV-1 transcription factor, as the protein that most efficiently interacts with viral G4s during infection. ICP4 specific and direct binding and unfolding of parallel G4s, including those present in HSV-1 immediate early gene promoters, induced transcription in vitro and in infected cells. This mechanism was also exploited by ICP4 to promote its own transcription. Proximity ligation assay allowed visualization of G4-protein interaction at the single selected G4 in cells. G4 ligands inhibited ICP4 binding to G4s. Our results indicate the existence of a well-defined G4-viral protein network that regulates the productive HSV-1 cycle. They also point to G4s as elements that recruit transcription factors to activate transcription in cells.
2021-09-10 | PXD024743 | Pride
Project description:G-quadruplex (G4) structures formed by guanine-rich nucleic acids are implicated in essential physiological and pathological processes and serve as important drug targets. The genome-wide detection of G4s in living cells is important for exploring the functional role of G4s but has not yet been achieved due to the lack of a suitable G4 probe. Here we report an artificial 6.7 kDa G4 probe (G4P) protein that binds G4s with high affinity and specificity. We used it to capture G4s in living human, mouse, and chicken cells with the ChIP-Seq technique, yielding genome-wide landscape as well as details on the positions, frequencies, and sequence identities of G4 formation in these cells. Our results indicate that transcription is accompanied by a robust formation of G4s in genes. In human cells, we detected up to >123,000 G4P peaks, of which >1/3 had a fold increase of ≥5 and were present in >60% promoters and ~70% genes. Being much smaller than a scFv antibody (27 kDa) or even a nanobody (12-15 kDa), we expect that the G4P may find diverse applications in biology, medicine, and molecular devices as a G4 affinity agent.
2020-10-13 | GSE133379 | GEO
Project description:G-quadruplex structures (G4s) have been identified in genomes of multiple organisms and proven to play important epigenetic regulatory roles in various cellular functions. However, the G4 formation mechanism remains largely unknown. Here, we found a negative correlation between DNA 5mC methylation and G4 abundance. The abundance of genomic G4s significantly increased when the whole-genome methylation level was reduced in DNMT1-knockout cells. This increase was then suppressed by DNMT1 over-expression. And more G4s were detected in the hypomethylated cancer cell line HepG2 and rectal cancer tissues. Besides, 5mC modification significantly inhibited G4 formation of the potential G-quadruplex sequences (PQSs). The transcription of genes with 5mC modification sites in their promoter PQSs was affected after treatment with G4 stabilizer pyridostatin or methylation inhibitor 5-aza-dC. The global reduction of genomic methylation elevates gene transcription levels through increased G4s. Taken together, DNA 5mC methylation prevents PQSs from folding into G4s in genomes.
2022-12-20 | GSE221436 | GEO
Project description:G-quadruplex structures (G4s) have been identified in genomes of multiple organisms and proven to play important epigenetic regulatory roles in various cellular functions. However, the G4 formation mechanism remains largely unknown. Here, we found a negative correlation between DNA 5mC methylation and G4 abundance. The abundance of genomic G4s significantly increased when the whole-genome methylation level was reduced in DNMT1-knockout cells. This increase was then suppressed by DNMT1 over-expression. And more G4s were detected in the hypomethylated cancer cell line HepG2 and rectal cancer tissues. Besides, 5mC modification significantly inhibited G4 formation of the potential G-quadruplex sequences (PQSs). The transcription of genes with 5mC modification sites in their promoter PQSs was affected after treatment with G4 stabilizer pyridostatin or methylation inhibitor 5-aza-dC. The global reduction of genomic methylation elevates gene transcription levels through increased G4s. Taken together, DNA 5mC methylation prevents PQSs from folding into G4s in genomes.
2022-12-20 | GSE221435 | GEO
Project description:Single-stranded genomic DNA can fold into G-quadruplex (G4) structures or form DNA:RNA hybrids (R loops). Recent evidence suggests that such non-canonical DNA structures affect gene expression, DNA methylation, replication fork progression and genome stability. When and how G4 structures form and are resolved remains unclear. Here we report the use of Cleavage Under Targets and Tagmentation (CUT&Tag) for mapping native G4 in mammalian cell lines at high resolution and low background. Mild native conditions used for the procedure retain more G4 structures and provide a higher signal-to-noise ratio than ChIP-based methods. We determine the G4 landscape of mouse embryonic stem cells (mESC), discovering G4 formation at active and poised promoters and enhancers. We discover that the presence of G4 motifs and G4 structures distinguishes active and primed enhancers in mESCs. Further performing R-loop CUT&Tag, we demonstrate the widespread co-occurence of single-stranded DNA, G4s and R loops, suggesting an intricate interrelation of non-canonical DNA structures, transcription and the formation and turnover of G4s.
2021-04-27 | GSE173103 | GEO
Project description:Four-stranded G-quadruplexes (G4s) are prevalent secondary structural features of the human genome. They are formed through stacking of Hoogsteen hydrogen-bonded G-tetrads connected by loops of variable length and sequence. G4 structures are found widely in genome control elements including gene promoters and are tightly linked to active gene expression and the recruitment of transcription factors and chromatin remodellers. To systematically investigate how G4 structures modulate transcription, we have developed a strategy in which different G4 sequences are engineered into the promoter of a synthetic reporter gene and ectopically into the same endogenous position in the genome of human cells. Here, we show that G4 sequences introduced into the host genome can fold into an G4 structure. Crucially, we demonstrate that G4 formation within a gene promoter stimulates transcription compared to G4-negative promoters and that this is not due to inherent G-richness. Finally, we provide robust evidence that transcriptional levels are directly related to the degree of thermodynamic stability of the G4 structure. Taken together, our results provide compelling evidence that G4 structures have a direct and positive regulatory role in gene transcription.
2024-02-21 | GSE241008 | GEO
Project description:Metazoan promoters are highly enriched in secondary structure forming motifs, among which G-quadruplexes (G4s). We describe G4access, a novel approach to isolate and sequence G4s when associated to open chromatin, based on their resistance to Micrococcal nuclease. G4access is an antibody- and crosslink-independent procedure that allows for high enrichment of predicted G4s (PG4s) motifs, most of which can be confirmed in vitro. Using this technique in several human and mouse cell lines, we were able to show a cell-specific enrichment that both relates to apparent nucleosome depletion and transcription at promoters. G4access allows scoring for PG4 pattern variation linked to nucleosome positioning changes that occur following treatment with a G4 ligand. It also reveals an unexpected role of G4s in hybrid mouse ES cells in the context of imprinting control regions, in which we propose that they will hallmark allelic active loci. Finally, we extended our procedure to non-mammalian species showing less annotated G4s in their genome. We found a decreased but still substantial G4 enrichment and confirmed their association to open and transcriptionally active regions of the yeast genome. Overall, our study not only provides a novel tool for studying G4 forming sequences in the cellular context but also indicates their essential roles as promoter elements, in chromatin opening and nucleosome positioning.
2023-04-14 | GSE187007 | GEO
Project description:G-quadruplexes (G4s) are unique noncanonical nucleic acid secondary structures, which could interact with transcription factors and chromatin remodelers to regulate cell type-specific transcriptome and shape chromatin landscapes. Based on the direct interactions between G4 and natural porphyrins, we established an in situ capture sequencing approach combining synthesized biotin-PEG4-Hemin and Cleavage Under Targets and Tagmentation (CUT&Tag) strategy to profile the Hemin binding sites in the human genome. We found that a proportion of G4s overlapped with Hemin binding sites and Hemin promoted genome-wide G4 formation at Hemin binding sites. Hemin treatments impaired gene transcription initiation and altered chromatin landscape with decreased H3K27ac and H3K4me3 modifications. Interestingly, G4 was not involved in the canonic Hemin-BACH1-NRF2-mediated enhancer activation process, highlighting an unprecedented G4-dependent mechanism for metabolic regulation of transcription. Furthermore, Hemin induced specific gene expression profiles in mouse primary hepatocytes, and block of Hemin degradation in mice by Hmox1 knockdown resulted in hepatic injury, providing in vivo insights for metabolic control of gene transcription by porphyrins.
2022-11-23 | GSE198658 | GEO